libvirt: Update instance machine type stash spec
* Replaces references to a new ``hw_machine_type`` Instance object attribute with the existing ``system_metadata`` dict. This was actually agreed to during the PTG but lost and replaced with the new attribute sometime later. * Drops the move of the hardcoded default machine types into the ``[libvirt]/hw_machine_type`` configurable as on review this is not actually required to achieve the goals of this spec and would if anything make things more complicated when upgrading. * Lists the new ``nova-manage`` commands and adds ``SHELVED`` as an allowed vm_state for the ``update_machine_type`` command. * Lists the default restrictions around updating the machine type via the ``update_machine_type`` outside of a full rebuild. These include between underlying machine types and from newer to older versions of the same machine type. * Adds a ``--force`` flag to the ``update_machine_type`` command to allow operators to workaround these restrictions. * Drops the reference to the versioned machine types from the data model impact section as we are now using ``system_metadata`` that forces us to use strings. * Replaces the incorrect ``SHUTOFF`` vm_state with the correct ``STOPPED`` state. * Replaces some incorrect uses of the term deployer and operator/admin with operator. Change-Id: I36d3b544afb33cdeb70dc3f2a9e067904ebfac05
This commit is contained in:
Lee Yarwood
Dan Smith
parent
8d78679dcc
commit
0d58760cdf
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@ -67,33 +67,33 @@ Use Cases
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default machine type for a given host architecture to make use of newer
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models of emulated hardware and features of QEMU.
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* As a deployer of an existing OpenStack environment I want to default a new
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machine type while not breaking the ABI of existing instances.
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* As an operator of an existing OpenStack environment I want to default to a
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new machine type while not breaking the ABI of existing instances.
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* As a user I want to ensure the ABI of my instance remains the same throughout
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the lifetime of the instance, regardless of default configurable changes made
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by deployers or developers.
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by an operator or virt driver developers.
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Proposed change
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===============
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* Copy the hardcoded machine type defaults from the libvirt driver into the
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``[libvirt]/hw_machine_type`` configurable.
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* Store the used machine type in the instance extras table during the initial
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spawn of the instance *or* init_host of the compute service for all running
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instances that don't have a ``machine_type`` listed at present.
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* Allow operators to set the machine_type of ``SHELVE_OFFLOADED`` instances via
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a ``nova-manage`` command.
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* Store the used machine type in the instance system metadata table during the
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initial spawn of the instance *or* init_host of the compute service for all
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running instances that don't have a ``hw_machine_type`` already stored.
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* Ensure the stored machine type is used during a hard reboot, move or any
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other action that results in the domain being redefined aside from a full
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rebuild of the instance.
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* Allow the stored machine_type of a ``SHUTOFF`` instance to be updated by
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an admin/operator via a ``nova-manage`` command. Allowing operators to
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migrate instances between versioned machine types if an alias is not used.
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* Unset the stored machine type during a rebuild allowing a new image defined
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machine type or host configured default to be used.
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* Allow operators to get the machine type of instances via a new
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``get_machine_type`` ``nova-manage`` command.
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* Allow operators to set or update the machine type of instances with a
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vm_state of ``STOPPED``, ``SHELVED`` or ``SHELVED_OFFLOADED`` via a new
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``update_machine_type`` ``nova-manage`` command.
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Alternatives
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------------
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@ -103,49 +103,9 @@ N/A
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Data model impact
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-----------------
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The ``Instance`` object will be extended to include a nullable
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``hw_machine_type`` attribute that maps to a simple ``StringField`` stored in
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the instance extras table.
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A ``StringField`` is used here as we cannot enumerate all of the possible
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values of machine_type as different distributions provide different
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versioned machine_types. For example Fedora provides machine types versioned by
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the underlying QEMU version, while RHEL provides machine types versioned by the
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underlying RHEL version::
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$ cat /etc/fedora-release
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Fedora release 33 (Thirty Three)
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$ qemu-system-x86_64 -machine help | grep q35
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q35 Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-5.1)
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pc-q35-5.1 Standard PC (Q35 + ICH9, 2009)
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pc-q35-5.0 Standard PC (Q35 + ICH9, 2009)
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pc-q35-4.2 Standard PC (Q35 + ICH9, 2009)
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pc-q35-4.1 Standard PC (Q35 + ICH9, 2009)
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pc-q35-4.0.1 Standard PC (Q35 + ICH9, 2009)
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pc-q35-4.0 Standard PC (Q35 + ICH9, 2009)
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pc-q35-3.1 Standard PC (Q35 + ICH9, 2009)
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pc-q35-3.0 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.9 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.8 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.7 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.6 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.5 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.4 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.12 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.11 Standard PC (Q35 + ICH9, 2009)
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pc-q35-2.10 Standard PC (Q35 + ICH9, 2009)
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$ cat /etc/redhat-release
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Red Hat Enterprise Linux release 8.2 (Ootpa)
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$ /usr/libexec/qemu-kvm -machine help | grep q35
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q35 RHEL-8.2.0 PC (Q35 + ICH9, 2009) (alias of pc-q35-rhel8.2.0)
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pc-q35-rhel8.2.0 RHEL-8.2.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel8.1.0 RHEL-8.1.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel8.0.0 RHEL-8.0.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel7.6.0 RHEL-7.6.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel7.5.0 RHEL-7.5.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel7.4.0 RHEL-7.4.0 PC (Q35 + ICH9, 2009)
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pc-q35-rhel7.3.0 RHEL-7.3.0 PC (Q35 + ICH9, 2009)
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The machine type will be stored within the ``Instance`` object under the
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``system_metadata`` field that is a ``DictOfNullableStringsField`` using the
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key ``hw_machine_type``.
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REST API impact
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@ -191,19 +151,19 @@ Upgrade impact
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When upgrading to Wallaby from Victoria (or earlier) on startup the libvirt
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driver will attempt to record the current machine type of each non-deleted
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instance residing on the host. This includes ``SHUTOFF``, ``PAUSED`` and
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instance residing on the host. This includes ``STOPPED``, ``PAUSED`` and
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``SHELVED`` instances. Where possible this will come from a direct query of
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the underlying guest domain but if one is not found it will instead come from
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the instance image metadata property ``hw_machine_type``,
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``[libvirt]/hw_machine_type`` configurable or legacy hardcoded defaults.
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For non-deleted instances that are marked as ``SHELVED_OFFLOADED`` and thus
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don't reside on a compute host a ``nova-manage`` command will be introduced
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that will allow operators/admins to record a machine type. As above this will
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rely first on any stored image properties but if non is found will require a
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specific machine type to be provided by the caller.
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don't reside on a compute host a ``update_machine_type`` ``nova-manage``
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command will be introduced that will allow operators to set a machine
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type. As above this will rely first on any stored image properties but if none
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is found will require a specific machine type to be provided by the caller.
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A ``nova-status`` command will be introduced to allow operators/admins to
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A ``nova-status`` command will be introduced to allow operators to
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determine when all non-deleted instances have had a machine type recorded
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across an environment.
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@ -211,14 +171,26 @@ While the aliased machine types (``q35`` for example) will be documented as the
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recommended choice admins and operators will be allowed to configure a
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versioned machine either per image or per architecture on a given compute host.
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As a result another ``nova-manage`` command will be introduced to update the
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machine type of a given ``SHUTOFF`` instance in the DB, allowing operators and
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admins to migrate instances between these versioned machine types overtime
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without a full rebuild of the instance. It should be noted that this
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command will not allow the machine_type to be changed between actual types of
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machine_type, for example ``pc`` to ``q35``. This will continue to require a
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full rebuild of the instance using a new image with associated
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``hw_machine_type`` image property set.
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As a result the same ``update_machine_type`` ``nova-manage`` command used to
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set the machine type of ``SHELVED_OFFLOADED`` instances will also be able to
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update the machine type of instances with a vm_state of ``STOPPED``,
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``SHELVED`` or ``SHELVED_OFFLOADED``.
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This will allow operators to migrate instances between these versioned machine
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types overtime without a full rebuild of the instance.
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It should be noted that by default this command will not allow the machine_type
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to be changed between actual types of machine_type, for example ``pc`` to
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``q35`` or between a newer and older version of a machine type.
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By default both will continue to require a full rebuild of the instance using a
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new image with associated ``hw_machine_type`` image property set or once the
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``[libvirt]/hw_machine_type`` defaults have been updated on the launching
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compute host.
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A ``--force`` flag will be inlcuded to allow operators to force through
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changes in both cases with a warning that the operation will likely break the
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ABI within the instance once restarted.
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Implementation
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==============
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@ -240,9 +212,6 @@ Feature liaison:
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Work Items
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----------
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* Copy the hardcoded machine type defaults into the
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``[libvirt]/hw_machine_type`` configurable.
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* Store the used machine type in the instance extras table during the initial
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spawn of the instance *or* init_host of the compute service for all running
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instances.
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@ -251,19 +220,22 @@ Work Items
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other action that results in the domain being redefined aside from a full
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rebuild of the instance.
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* Introduce a ``nova-manage`` command to allow operators and admin to set
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the recorded machine_type for non-deleted ``SHELVE_OFFLOADED``
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instances.
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* Unset the stored machine type during a rebuild allowing a new image defined
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machine type or host configured default to be used.
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* Introduce a ``get_machine_type`` ``nova-manage`` command to allow operators
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to get the recorded machine_type of an instance.
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* Introduce a ``update_machine_type`` ``nova-manage`` command to allow
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operators to set or update the recorded machine_type for a given instance
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with a vm_state of ``STOPPED``, ``SHELVED`` or ``SHELVED_OFFLOADED`` allowing
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upgrades between versioned machine types over time.
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* Introduce a ``nova-status`` upgrade check to ensure the machine_type has
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been updated for all instances residing on a given host in the env or across
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all hosts.
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* Introduce a ``nova-manage`` command to allow operators and admin to update
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the recorded machine_type for a given instance, allowing upgrades between
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versioned machine types over time.
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* Write extensive operator/admin documentation for the above.
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* Write extensive operator documentation for the above.
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Dependencies
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============
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@ -276,14 +248,10 @@ Testing
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The ``grenade`` job will be extended to ensure the machine_type field is
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being populated during compute service startup when using the libvirt driver.
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Functional tests should also be written to assert the above and failure
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behaviour when attempting to change the default before a machine_type has
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been registered for all instances on a given compute.
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Documentation Impact
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====================
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Operator/admin documentation covering the upgrade impact and use of the
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Extensive operator documentation covering the upgrade impact and use of the
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configurable will be written.
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References
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